Environmental change in Greater Australia.

Environmental change in Greater Australia. Australia, a dry island continent in mid latitude, spans fromtropical to cold temperature regions; long isolation has given it itsown flora and fauna. Environment changes in the late Quaternary quaternary/qua��ter��nary/ (kwah��ter-nar?e)1. fourth in order.2. containing four elements or groups.qua��ter��nar��yadj.1. Consisting of four; in fours. have hadtheir own and special courses in the continent and its several regions.The role of fires set by people is an important issue in the changing`natural' landscape. Globally, the Pleistocene - Holocene transition incorporated someof the most dramatic environmental changes in earth's history. Itextended from the height of the last glacial period, when ice sheetscovered about 30% of the earth's surface (Williams et al. 1993 andsea-level was estimated to have been c. 120 m lower than today(Fairbanks 1989), to the attainment of approximately present-dayconditions. These changes were achieved in about 11,000 radiocarbonyears from c. 17,000 to 6000 b.p.; noted discrepancies betweenradiocarbon and uranium-series dates on submerged corals around Barbadosrecently used to date sea-level rise suggest that the transition mayhave begun at least 2000 years earlier (Bard et al. 1990). However, asmost data for this period are based on radiocarbon dates, theconventional radiocarbon time-scale is retained in this paper. A recent global comparison of various palaeoclimatic data andsimulations from general circulation models concluded that the majorinfluences on climates during the transition period were deglaciation de��gla��ci��a��tion?n.The uncovering of glaciated land because of melting or sublimation of the glacier.deglaciation?The uncovering of land that was previously covered by a glacier. and variations in the seasonal and latitudinal distribution of solarradiation caused by changes in earth-sun geometry (Webb et al. 1993).These influences combined to produce marked regional differences inclimatic amelioration a��me��lio��ra��tion?n.1. The act or an instance of ameliorating.2. The state of being ameliorated; improvement.Noun 1. through their effects on atmospheric and oceaniccirculation patterns. Australia, although geographically divorced fromthe major Northern Hemisphere ice sheets, still experienced substantialenvironmental change, with the climatic component perhaps augmented bythe impact of people. A number of studies indicate that initial burningby Aborigines aborigines:see Australian aborigines. was sufficient to increase the distribution offire-promoting vegetation, particularly eucalypt woodlands and forests,and lead to substantially greater environmental instability thanexperienced in other non-glaciated parts of the world and also duringprevious climatic cycles within Australia. The effect of thisinstability, in the form of increased erosion, sand-dune activity, andsalinity and greater variability in river flow patterns, would have beengreatest towards the end of the Pleistocene when conditions weregenerally much drier than today (Kershaw 1989). Conversely, thecontinuation of burning in the Holocene may have prevented theachievement of potential post-glacial amelioration. The period is alsodistinguished from previous transitions in lacking the impact of amegafauna meg��a��fau��na?n. (used with a sing. or pl. verb)Large or relatively large animals, as of a particular region or period, considered as a group.meg that may also have succumbed to the activities of people(Flannery 1994). Present day environments Australia is characterized by its isolation in the mid-to-lowlatitudes of the Southern Hemisphere; it has ancient, weathered andlow-lying land surfaces, widespread aridity and climatic variability,and a high and widespread incidence of fire. These features have led tothe evolution of a vegetation cover dominated by sclerophyllouswoodlands and shrublands with eucalypts, casuarinas and phyllodinousacacias, taxa largely confined to the continent, and the morecosmopolitan Chenopodiaceae in saline areas, as major canopy components(Figure 1). Mesic communites are confined to the better-watered andfrequently more fertile and mountainous southwestern corner, northernmargin and east coast where rainforest communities or elements survivein locally wet or fire-protected patches surrounded byeucalypt-dominated sclerophyll Sclerophyll is a type of vegetation that has hard leaves and short internodes (the distance between leaves along the stem). The word comes from the Greek sclero (hard) and phyllon (leaf). forests. Herbaceous her��ba��ceous?adj.1. Relating to or characteristic of an herb as distinguished from a woody plant.2. Green and leaflike in appearance or texture. or grasslandcommunities are restricted to heavy soils such as the alluvial plains ofthe Great Artesian Basin Great Artesian Basin,c.670,000 sq mi (1,735,300 sq km), between the Eastern Highlands and the Western Plateau, E central Australia, extending S from the Gulf of Carpentaria, Queensland, to NE South Australia and N New South Wales. and in parts of the volcanic western plains ofVictoria, to the nutrient-poor quartzites of the wet southwest ofTasmania and to small areas of alpine vegetation in the very southeastof the continent. By contrast, a large part of the island of New Guinea New Guinea(gĭn`ē), island, c.342,000 sq mi (885,780 sq km), SW Pacific, N of Australia; the world's second largest island after Greenland. has a younglandscape, dominated by high mountains and a uniformly wet climate,which supports widespread rainforest and significant areas of alpinevegetation and small remnant glaciers above the tree line.Characteristic Australian vegetation, represented by woodlands, islargely confined to the southern margin. The data-base A wide range of techniques have been used to reconstruct Australianlate Quaternary environments, with varying degrees of success, accuracy,and geographical and temporal coverage. Studies of morphological andsedimentological aspects of desert dunes and of glacial and periglacial ''You may be looking for paraglacial, meaning unstable conditions related to local glaciation in the recent past.Periglacial is an adjective referring to places in the edges of glacial areas, normally those related to past ice ages rather than those in the modern era. features provide some of the best evidence for climates existing withinarid regions and on high mountains respectively for the last glacialperiod, and limited information on subsequent Holocene conditions.Studies on coastal land-forms provide evidence of the changing extentand degree of fragmentation of the Australian land-mass through time. Inrecent years, with the development of dating methods such asthermoluminesence, gross patterns of change in fluvial flu��vi��al?adj.1. Of, relating to, or inhabiting a river or stream.2. Produced by the action of a river or stream.[Middle English, from Latin systems have beendetermined from the examination of alluvial sequences within a broadrange of environments. By far the most data have been derived from the study of sedimentsand contained fossils associated with aquatic basins which, althoughgenerally unrepresentative Adj. 1. unrepresentative - not exemplifying a class; "I soon tumbled to the fact that my weekends were atypical"; "behavior quite unrepresentative (or atypical) of the profession" of the landscapes in which they are found,frequently yield continuous records through much of thePleistocen-Holocene transition. In the more humid parts of the continentextending into the adjacent oceans, pollen analysis Analysis of the distribution of pollen grains of various species contained in surface layer deposits, especially peat bogs and lake sediments, from which a record of past climate may be inferred. of aquaticsediments, which has included an examination of charcoal in recentyears, has been the major analytical tool and usefully providesinformation on whole catchment areas. At a number of sites,complementary data on local aquatic conditions, particularlylake-levels, have been obtained from lake-dwelling biota biota/bi��o��ta/ (bi-o��tah) all the living organisms of a particular area; the combined flora and fauna of a region. bi��o��tan.The flora and fauna of a region. of whichostracods and diatoms have proved to be of greatest value.Sedimentological analyses of lakes and associated lunettes are importantin drier areas; along with limited palaeoecological examination of cavesediments and some swamps, they provide the small number ofpalaeoenvironmental records that relate directly to archaeologicalexcavations. Pollen and lake-level data have formed the basis for recentreconstructions of late Quaternary climates in, or incorporating, theGreater Australian region (Harrison & Dodson 1993; Markgraf et al.1992); they are emphasized in this paper. Areas where a sufficientnumber of sites have been analysed to allow the construction of aregional picture are shown in Figure 2. These include: the highlands ofNew Guinea, the Barrington Tops of northern New South Wales New South Wales,state (1991 pop. 5,164,549), 309,443 sq mi (801,457 sq km), SE Australia. It is bounded on the E by the Pacific Ocean. Sydney is the capital. The other principal urban centers are Newcastle, Wagga Wagga, Lismore, Wollongong, and Broken Hill. and theGreat Australian Bight Great Australian Bight,wide bay of the Indian Ocean, indenting the southern coast of Australia. An unbroken line of cliffs c.200 ft (60 m) high runs along the coast and extends inland as the arid and desolate Nullarbor Plain. where reconstructions are based almost entirelyon pollen data; the humid tropics tropics,also called tropical zone or torrid zone, all the land and water of the earth situated between the Tropic of Cancer at lat. 23 1-2°N and the Tropic of Capricorn at lat. 23 1-2°S. region of north-east Queensland,southeastern mainland Australia and Tasmania that incorporate asignificant component of lake-level data, and the southeast interiorwhere the reconstructions of Harrison (1989; Harrison & Dodson 1993)are derived predominantly from lake-level data. A reasonable amount ofinformation from the southwest of Western Australia Western Australia,state (1991 pop. 1,409,965), 975,920 sq mi (2,527,633 sq km), Australia, comprising the entire western part of the continent. It is bounded on the N, W, and S by the Indian Ocean. Perth is the capital. currently defies thedevelopment of a consistent regional record. A number of individualsites identified on Figure 2 broaden the continental picture; there isstill a dearth of information from large parts of the continent,especially the arid and sub-arid regions and most of its western half.To assist with record comparisons, inferred climate curves for the lateQuaternary derived from some regions are presented in Figure 3. The pollen data-set assembled for selected time-slots through thelate Quaternary within mainland southeastern Australia (Figure 4) showspatterns of change in greater detail (Kershaw et al. 1994, unpublisheddata). Information from 71 pollen diagrams is included, coveringenvironments from sea-level to c. 2000 m altitude, a mean annualprecipitation range of 1600 mm and a mean annual temperature range of 13[degrees]C, although only 12 diagrams provide evidence for alltime-slots. Average pollen values of selected taxa for (each timeslot,based on a pollen sum of some 14 major dryland taxa, are shown on Figure5, while changing distribution and abundance values for some of thesetaxa are mapped on Figure 6. The height of the last glacial period Australia, in common with all continents, experienced a greatercoverage of ice during the last glacial period. Ice sheets or cirqueswere centred on those areas now displaying alpine vegetation (see Figure1). However, glaciation was limited and had only local influence onclimate, vegetation and presumably pre��sum��a��ble?adj.That can be presumed or taken for granted; reasonable as a supposition: presumable causes of the disaster. people. Glaciers covered c. 2000-2200sq. km of the high mountains of New Guinea, 19-32 sq. km in the MountKosciusko region of the Snowy Mountains Snowy Mountains,range of the Australian Alps, SE Australia. It is the site of the Snowy Mts. Hydroelectric Scheme, Australia's most extensive hydroelectricity and irrigation complex. The scheme was begun in 1949 and completed in 1972. , and in excess of 2000 sq. km inTasmania (Colhoun & Peterson 1986). Snow-lines were reduced by atleast 1000 m in altitude in all areas. Temperatures were some 7[degrees]C lower than present in highland New Guinea, and at least 6[degrees] and possibly up to 10 [degrees]C lower in southeasternAustralia. In New Guinea, pollen evidence indicates that expansion of ice wasaccompanied by largely equivalent depressions in altitude of the majorvegetation belts. The tree-line was at least 900 m lower and up to anestimated 1700 m lower in some areas (Hope & Golson, this volume),while the boundary between the lower montane mon��tane?adj.Of, growing in, or inhabiting mountain areas.[Latin montnus, from m and lowland rainforest mayhave been 600 to 780 m lower.(1)(1) These data appear inconsistent with CLIMAP CLIMAP Climate/Long Range Investigation Mappings and Predictions Project project members'(1981) estimates, based on planktonic plank��ton?n.The collection of small or microscopic organisms, including algae and protozoans, that float or drift in great numbers in fresh or salt water, especially at or near the surface, and serve as food for fish and other larger organisms. microfossil mi��cro��fos��sil?n.A microscopic fossil, as of a pollen grain or unicellular organism.microfossil?A microscopic fossil, as of a pollen grain or unicellular organism.Noun 1. records from oceancores, for sea-surface temperatures within 2 [degrees]C of today'svalues in tropical latitudes. Although little information was derivedfrom this region, a recent estimated decrease of no more than 1.5[degrees]C for the western tropical Pacific Ocean from the molecularanalysis of alkenones preserved in marine sediments (Ohkouchi et al.1994) provides support for the CLIMAP estimates. Unfortunately there isno evidence of temperatures from terrestrial lowland sites in theAustralasian tropics during the Last Glacial Maximum The Last Glacial Maximum (LGM) refers to the time of maximum extent of the ice sheets during the last glaciation (the W��rm or Wisconsin glaciation), approximately 20,000 years ago. This extreme persisted for several thousand years. to resolve this;bioclimatic bi��o��cli��ma��tol��o��gy?n.The study of the effects of climatic conditions on living organisms.bi estimates from pollen data for oxygen isotope Stage 3 in theLynch's Crater record of northeast Queensland suggest thattemperatures may have been little different from those of today at thattime (Kershaw & Nix 1989). By contrast, sea-surface temperaturesderived from oxygen-isotope analysis of uplifted coral reefs on the Huonpeninsula Huon Peninsula is a large peninsula in Morobe Province, eastern Papua New Guinea, at . It is named after French explorer Jean-Michel Huon de Kermadec. The peninsula is dominated by the Saruwaged Range. of New Guinea indicated a 3 [degrees]C lower temperatureduring oxygen-isotope Stage 3 (Aharon & Chappell 1986), and suggestthat temperatures may have been at least 5 [degrees]C lower than todayat the Last Glacial Maximum. In southeastern Australia, sea-surface temperatures are estimatedto have been 2-4 [degrees]C lower than today, values consistent withthose from the ice caps and glaciers assuming a slightly higheradiabatic lapse rate lapse raten.The rate of decrease of atmospheric temperature with increase in altitude.lapse rate?The rate of change of any meteorological phenomenon, especially atmospheric temperature with altitude. under effectively lower precipitation levels.Reduced temperatures from lower-altitude terrestrial environments areinferred from the dominance of grassy subalpine herbland and coniferous con��i��fer?n.Any of various mostly needle-leaved or scale-leaved, chiefly evergreen, cone-bearing gymnospermous trees or shrubs such as pines, spruces, and firs. scrub in a marine pollen record off southwestern Tasmania (van dee Geeret al. 1994), and alpine shrub and herb taxa, identified to specieslevel, from macrofossil mac��ro��fos��sil?n.A fossil large enough to be examined without a microscope. remains at Spring Creek A spring creek is a stream that flows from a spring. Spring Creek may refer to any of the following specific places: Spring Creek, Arkansas Spring Creek, California Spring Creek (Colorado), a tributary of the Cache La Poudre River Spring Creek, Florida in lowland westernVictoria (Flannery & Gott 1984). Assessment of temperatures throughmost of this region from pollen analysis is prevented by a break-uprather than an altitudinal depression of forest belts. It can be seen onFigure 6, from those records extending back to the Last Glacial Maximum,that much of southeastern mainland Australia was covered by a fairlyhomogeneous Poacea - Asteraceae steppe steppe(stĕp), temperate grassland of Eurasia, consisting of level, generally treeless plains. It extends over the lower regions of the Danube and in a broad belt over S and SE European and Central Asian Russia, stretching E to the Altai and S to . The low but widespread valuesfor the canopy dominants of present forest and woodland vegetation,Eucalyptus and Casuarina casuarinaAny of the chiefly Australian trees that make up the genus Casuarina (family Casuarinaceae), which have whorls of scalelike leaves and segmented stems resembling horsetails. Several species, especially C. , suggest survival in suitable microhabitatsrather than wholesale migration to more hospitable regions. Only onesite, Boulder Flat in East Gippsland, has eucalypt values suffientlyhigh to indicate the location of a `refugium' and this site is in asheltered area at low altitude on a river draining the eastern highlands Eastern Highlands,c.2,400 mi (3,860 km) long, general name for the mountains and plateaus roughly paralleling the east and southeast coasts of Australia (including Tasmania) and forming the Continental Divide (see Great Dividing Range); rises to Mt. (Kenyon 1989). Data for Pomaderris and Nothofagus are even more sparse,suggesting the lack of identifiable wet sclerophyll forests andrainforests respectively. However, a recent analysis of a pollen sitewithin Nothofagus forest in the Otway Ranges does indicate the survivalof that taxon taxon(pl. taxa), in biology, a term used to denote any group or rank in the classification of organisms, e.g., class, order, family. in that place, albeit over a much reduced area, throughthe height of the last glacial (Merna McKenzie, pers. comm.). Although temperatures were lower than present over much ofsoutheastern mainland Australia, they were not sufficiently low toexplain the lack of tree growth over most of the area (Hope 1989). Evidence for reduced precipitation includes generally higher levelsthan today of pollen of salt-tolerant Chenopodiaceae and the lack oforganic sedimentation and pollen preservation in many pollen sites.However, some sites such as Northwest Crater at Tower Hill on thepresent-day southwest Victorian coastline (D'Costa et al. 1989) andLake Bolac in the drier part of the Victorian western plains (Crowley& Kershaw 1994) did maintain at least shallow water See: Shallow water blackout Waves and shallow water Shallow water equations Shallow Water, Kansas through theheight of the last glacial. At the latter site the water was also fresh,in comparison to the very saline nature of the lake today. Furthernorth, in the southeastern interior, a number of lakes show water levelsas high or higher than today, although some were drier (Harrison ADodson 1993). Harrison & Dodson consider, within this region, theclimate was generally as wet or wetter than present. A similar mixedpicture is provided by fluvial activity is southeastern Australia. Ingeneral, rivers were not particularly active except on the inland plainsthat received seasonal snow melt from the Snowy Mountains (Nanson et al.in press). By contrast, drier conditions, with precipitation perhaps less thanhalf of that of today, are proposed for much of the central part of thecontinent, extending through the southeast interior and southeasternmainland Australia to northern Tasmania, from the activity of desertdunes (Wasson 1989). Radiocarbon and thermoluminescence thermoluminescenceEmission of light from certain heated substances as a result of previous exposure to high-energy radiation. The radiation causes displacement of electrons within the crystal lattice of the substance. dates for thisactivity, scattered from 31,000 to 9000 b.p., peak around 20,000 b.p.(Wasson 1986). In addition to aridity, there must have been a sparservegetation cover and greater wind speeds. Reduced precipitation isclearly reflected in the Nullarbor Plains sites with Chenopodiaceousshrublands occupying areas now dominated by mallee eucalypt vegetation(Martin 1973). However, it is argued by Martin (1993) that lowermoisture levels are due to the greater distance of sites from the coastand that regional precipitation levels were similar to those of today.Lake-levels in the southwest of Western Australia were low (Harrison ADodson 1993). There is clearly a problem, assuming accurate dating of sequences,how can there be all at the same time higher lake-levels, dune activityand treelessness in, at least, parts of southeastern Australia? Oneexplanation, put forward by Prentice et al. (1992) to explain a similarconflict between evidence for widespread steppe and high lake-levelsduring the height of the last glacial period in the Mediterraneanregion, is the existence of a summer-dry, winter-wet climate with excesswinter rain producing run-off that filled the lakes, andevapotranspiration evapotranspirationLoss of water from the soil both by evaporation from the soil surface and by transpiration from the leaves of the plants growing on it. Factors that affect the rate of evapotranspiration include the amount of solar radiation, atmospheric vapor pressure, in relatively warm summers sufficient to exclude thegrowth of trees and presumably to facilitate sand movement. Thisscenario, not inconsistent with the warm, dry, windy summers postulatedfor the region by Bowler & Wasson (1984), is supported by localpollen data from southeastern Australia where high levels of the aquaticMyriophyllum (see Figure 6) suggest shallow and fluctuating water levelsgenerally. The low percentages of the predominantly bog plantRestionaceae further indicate the lack of a stable water level requiredfor successional change to this hydroseral level. In fact, throughoutAustralia there is little evidence for swamp or bog communites duringthe height of the glacial period. Further light on this glacial problem is provided by the combinedpollen and lake-level record from Lake Frome Lake Frome () is a large endorheic lake in South Australia, east of the Northern Flinders Ranges. It is a large, shallow, unvegetated playa or saltpan, 100 km long and 40km wide, lying mostly below sea level and having a total surface , which suggests substantialvariation in effective precipitation during the height of the glacialperiod (Bowler 1986; Singh & Luly 1991). The lake was dry before c.18,000 b.p.; water levels then increased until c. 17,000 b.p.; and thelake remained wet until c. 14,500 b.p. Cheno podiaceae dominated thevegetation initially, then Callitris woodland became more important. Thehigh proportion of temperate plants indicates temperatures lower thantoday while a high Chenopodiaceae/Poaceae pollen ratio is interpreted asindicating a winter rainfall regime, consistent with the hypothesis ofPrentice et al. (1992). The general lack of fluvial activity in the Carpentaria Basin(Nanson et al. 1991) and low lake-levels, combined with the existence ofsclerophyll woodland around Lynch's Crater (an area now supportingcomplex rainforest), suggests that the present terrestrial part ofnortheastern Australia was relatively dry. Rainfall around Lynch'sCrater was considered to be less than half present-day levels (Kershaw1976). It is probable that rainforest, even within perhumid areas, wasreduced to small isolated patches, as even proposed refugial areas havebeen found, from dated and taxonomically identified soil charcoal, tohave supported eu calypt woodland (Hopkins et al. 1993). Aridity alsoextended on to the exposed continental shelf with open woodlandspredominant around Lake Carpentaria (Torgerson et al. 1988) and on theshelf adjacent to the wet tropics (Grindrod pers. comm.). Although thereis little evidence from the vegetation for drier conditions in the NewGuinea highlands The New Guinea Highlands, also known as the Central Range or Central Cordillera, are a chain of mountain ranges and intermountain valleys on the island of New Guinea which run generally east-west the length of the island. , peaks in charcoal in some sites suggest that theregion may have been prone to fire at this time (Kershaw et al. inpress). In this perhumid environment. supporting few dry-adapted plants,a significant reduction in rainfall could perhaps occur without aconcomitant change in the vegetation. Somewhat drier conditions would,to some degree, increase the adiabatic lapse and help reconcile theglacial period temperature disparity between mountains and sea-levels inthis region. The Transition 1: the 'late glacial' This period from the time of glacier melting to the Pleistocene -Holocene boundary was globally one of rapid environmental change and onenoted for marked climatic reversals such as the very topical YoungerDryas stadial dated between 11,000 and 10,000 b.p. (Rind RINDSee Reversible ischemic neurological disability. et al. 1986). In the Australian region, amelioration after the height of the lastglacial is most clearly marked by the beginning of organic sedimentationin previously glaciated or periglaciated areas and by pollen changes inadjacent areas. In New Guinea the best-documented evidence is from theMount Jaya area in Irian Jaya Irian Jaya,province, Indonesia: see Papua. and Mount Wilhelm Mount Wilhelm (German: Wilhelmsberg) is the highest mountain in Papua New Guinea at 4,509 metres. It is part of the Bismarck Range and the peak is the point where three provinces intersect, Simbu, Western Highlands and Madang. in Papua New Guinea Papua New Guinea(păp`ə, –y ,where ice retreated from c. 15,000 b.p., and had effectively disappearedby 9,000 b.p. (Hope & Peterson 1975; Hope 1976). In southeasternAustralia, dates from within and marginal to the area of glaciation inthe Snowy Mountains indicate rapid deglaciation at or slightly before15,000 b.p. (Costin 1972); in Tasmania retreat commenced sometime before14,000 years b.p. and ice had effectively disappeared by 10,000 b.p.(Colhoun A Peterson 1986). In New Guinea the upward migration or reconstitution of montanecommunites suggests a gradual increase in mean annual temperature fromthe height of the last glacial to 12,000 b.p. (Walker &, Flenley1979) although a substantial rise in the tree-line noted from the studyof highland sites suggests more rapid amelioration to conditions similarto those of today between 10,500 and 8500 b.p. (Haberle 1994; Walker& Hope 1982). In Tasmania there is debate over the pattern ofamelioration, based largely on the factors controlling the successionfrom alpine vegetation to forest. From the pollen analysis of a numberof high-altitude sites, Macphail (1979) concluded that a major increasein temperature between about 11,500 and 9,500 b.p. was largelyresponsible for the expansion firstly of eucalypt vegetation and thenrainforest. Markgraf et al. (1986) refined this interpretation bysuggesting that rising temperatures resulted in the development ofshrub-dominated communities after 12,000 b.p. which changed into moreclosed rainforests after 11,000 b.p. Conversely Colhoun et al. (1991)argue from the rapid changes from alpine/sub-alpine through eucalyptvegetation to rainforest at the lowland site of Governor Bog in westernTasmania, that temperatures may have increased some 5[degrees]C topresent-day levels from just prior to 12,500 b.p. or slightly earlier.They consider that the later timing and different rates of succession athigher-altitude sites could have been controlled more by soil types andby migration rates from forest 'refugia' rather than byclimate change. A compromise of stepped increases in temperature duringthe late glacial period, as also inferred for the Central Highlands Central Highlands is the name for several mountainous regions located in the center of the nations or geographical regions. Central Highlands (Central America) Central Highland (France) Central Highlands (Iceland) ofVictoria, is shown in Figure 3. Patterns of vegetation change in relation to temperature withinwestern Tasmania are complicated, at least in the less humid sites, bymoisture levels some 20% lower than those of today (MacPhail 1979).Markgraf et al. (1986) also consider there is evidence for markedseasonal water stress centered on 12,000 b.p., a date identified as thetime of lowest lake water levels during the transition in all studiedlakes in Tasmania and coastal southeastern mainland Australia, and inmost lakes in the southeastern interior (Harrison & Dodson in 1993).Data for 12,000 b.p. from the southeastern Australian pollen-set providefurther support for dry conditions, with Chenopodiaceae values beinghighest and Myriophyllum values the lowest for the whole documentedperiod (Figure 5). Together they indicate dry and frequently saline linewater bodies. Dry conditions are also indicated from the predominance ofherbaceous communites. Within these communities, Poaceae isproportionately much better represented than Asteraceae in comparison tothe height of the glacial. This would suggest a change from steppe tograssland under increased temperatures. The increase in eucalypt values in the better-watered highlands andlack of response in woodland or forest taxa in the drier western part ofmainland southeast Australia is consistent with a temperature controlover forest expansion. There is little indication of the degree ofaridity at this time; the remains of red kangaroo The Red Kangaroo (Macropus rufus) is the largest of all kangaroos and the largest surviving marsupial. It is found across mainland Australia, avoiding only the more fertile areas in the south, the east coast, and the northern rainforests. dated to c. 12,640b.p. in the Lake Bolac lunette lu��nette?n.1. Architecturea. A small, circular or crescent-shaped opening in a vaulted roof.b. A crescent-shaped or semicircular space, usually over a door or window, that may contain another window, a suggests that here, rainfall was at least50-60% lower than the present-day estimate of 516 mm (Horton 1984).Obviously with sediment deflation from lakes in the Bolac region, nolake pollen record is preserved from this time-period (Crowley &Kershaw 1994). The duration of these drier conditions in southern Australiaappears to have been regionally variable. Lakes in the interior ofsoutheastern Australia and southwestern Australia achieved peaks of highlake-levels between c. 15,000 and c. 14,000 b.p. before falling, whilethe pollen record from Lake Frome suggests dry conditions between c.14,500 and c. 13,000 b.p. Dates from the continuous Tower Hill recordsuggest that the dry phase in more coastal parts of southeasternAustralia may have extended from 15,000 to 11,500 b.p. Lakes in Tasmaniawere beginning to rise by 11,000 b.p. In northern Australia The term northern Australia is generally considered to include the States and territories of Australia of Queensland and the Northern Territory. The part of Western Australia (WA) north of latitude 26�� south — a definition widely used in law and State government policy , available evidence from the AthertonTableland The Atherton Tableland is a fertile plateau which is part of the Great Dividing Range in Queensland, Australia. It is located west to south-south-west inland from Cairns, well into the tropics, but its elevated position provides a climate suitable for dairy farming. and Lake Carpentaria indicates the persistence of openeucalypt woodland under dry conditions. There is some indication fromthe very slow sediment accumulation rate in Lynch's Crater thatdriest conditions occurred between c. 15,000 and c. 10,500 b.p. Supportfor these dry conditions may be provided by the humid tropics soilcharcoal study of Hopkins et al. (1993) where dates on charcoal peakbetween c. 15,000 and 7,500 b.p. In New Guinea reduced effectiveprecipitation is suggested between c. 13,000 and 11,500 b.p. There is no evidence for a period of climatic change Climatic Change is a journal published by Springer.[1] Climatic Change is dedicated to the totality of the problem of climatic variability and change - its descriptions, causes, implications and interactions among these. that canunequivocally be related to the Younger Dryas stadial. However, themajority of sequences extending through the late glacial are generallyvery condensed and lack easily dated material which has inhibitedspecific investigation of this phenomenon. De Deckker et al. (1991) dosuggest that, within the Lake Carpentaria record, a peak in aeolian Ae��o��li��an?adj.1. Of or relating to Aeolis or its people or culture.2. Greek Mythology Of or relating to Aeolus.3. aeolian Variant of eolian.n.1. dustdated between c. 11,375 and c. 10,430 b.p. was likely to represent a dryphase related to Younger Dryas cooling, but this was only one of anumber of such events which had occurred with a periodicity periodicity/pe��ri��o��dic��i��ty/ (per?e-ah-dis��i-te) recurrence at regular intervals of time. pe��ri��o��dic��i��tyn.1. of about2250 years through much of the last 30,000 years. Recently, a large fallin atmospheric [C.sup.14]/[C.sup.12], recorded in the Huon Peninsulacoral record of northern New Guinea, has been considered to providefurther evidence for the Younger Dryas within this region (Edwards etal. 1993). The Transition 2: the Pleistocen-Holocene boundary This boundary, conventionally dated at 10,000 radiocarbon yearsb.p., is not considered a dominant feature of the transition period inAustralian archaeology (Frankel 1993; this volume; Pardoe 1993).However, it is clearly marked as a time of rapid climatic change in mostregional reconstructions (Figure 3) with temperature and/orprecipitation reaching close to present/day values. It is a time when asignificant number of palaeocological records are initiated and, from acompilation of dated sedimentary histories for 42 peatlands insoutheastern mainland Australia (Kershaw et al. 1993), a preferred timefor change in sediment type and, particularly, the formation of peat(Figure 7). Taking a less rigid definition of this boundary, the period between12,000 and 9,000 b.p. in southeastern mainland Australia records thegreatest changes in pollen assemblages, and hence vegetation, within thelast 18,000 years. Regionally, eucalypt vegetation expandedsubstantially with percentages through the southeastern highlands region Highlands Region is one of four regions of Papua New Guinea.It comprises: Southern Highlands Enga Province Western Highlands Simbu Eastern Highlands See alsoPapua Region Islands Region Momase Region indicating a change from woodland to forest form. In the drier westernpart of the region and in present coastal areas, Casuarinaceae forestsand woodlands largely replaced pre-existing grasslands. Grasses survivedover most of the region, as the dominant understorey, but Asteraceaelevels, probably through the elimination of steppe and alpineherbfields, suffered a substantial decline. Similar changes occurred inthe Tasmanian highlands with transitions here from alpine vegetationthrough eucalypt forests to rainforest (Markgraf et al. 1986), in theBarrington Tops where eucalypt forest replaced steppe-like vegetation(Dodson et al. 1986), and in New Guinea where altitudinal vegetationbelts rose substantially c. 10,500 b.p. (Haberle 1994). On the AthertonTableland, amelioration was marked only by increases in lake waterlevels. Open eucalypt woodland continued to dominate the landscape. There is conflict between the dating of events in the two pollenrecords from Lake Frome (Singh 1981; Singh & Luly 1991), but theinferred change from Chenopodiaceae to a Poaceae-dominated understoreyin this semiarid landscape, suggests to them a change from a winter to asummer rainfall Pattern, which may have occurred c. 10,000 b.p. The Transition 3: the early to mid Holocene This period, witnessing the later part of the post-glacial marinetransgression, was one of continuing climatic amelioration in mostregions, generally culminating in levels of temperature and/orprecipitation higher than those of today, a denser vegetation cover anda high degree of environmental stability. However, there appears to havebeen much regional variation in rates of amelioration and timing, and,within some areas, the degree of correspondence between'optimum' conditions for various parameters. In New Guinea, climatic conditions similar to those of today wereachieved c. 10,000 b.p. with an absence of ice between c. 9,000 and5,000 b.p. (Hope & Peterson 1975) and the greatest development offorest and shrublands between 8600 and 5000 b.p. (Harrison & Dodson1993) indicating this as the period of highest temperatures. Within theregion there is some spatial variation (Hope & Golson, thisvolume). In northern Australia effective precipitation was the majorinfluence on landscape features. Although lake-levels began to rise from10,000 b.p., maximum levels were not achieved until c. 8000 b.p. on theAtherton Tableland (Kershaw 1979) and 75000 b.p. on Groote Eylandt Groote Eylandt(grt ī`lənd)[Du.,=large island], 950 sq mi (2,461 sq km), Northern Territory, N Australia. (Shulmeister 1992). The commencement of fluvial activity in theCarpentaria Basin indicates that this precipitation increase was a broadregional feature. A detailed pollen and charcoal record from LakeBarrine Lake Barrine is a freshwater lake stituated on the Atherton Tableland in Far North Queensland, Australia, close to Lake Eacham.Lake Barrine was formed over 17,000 years ago when a large volcano erupted, leaving a crater that over time filled up with water to create a lake. on the Atherton Tableland demonstrates the survival of openeucalypt woodland under a regime of regular burning until c. 9000 b.p.,after which it was replaced, under increased precipitation, by wetsclerophyll forest maintained by fewer but more intense fires until c.7000 b.p. when rainforest expanded over the catchment (Walker & Chen1987). It is considered that burning may have inhibited an earlierrainforest expansion (Walker & Chen 1987), a hypothesis supported,to some degree, by lake-level data and regionally by the maintenance ofhigh levels of soil charcoal (Hopkins et al. 1993). On Groote Eylandt,open eucalypt forest replaced the preexisting open woodland c. 7500 b.p.High effective precipitation on both Groote Eylandt and the AthertonTableland was maintained until after 4000 b.p., with maximum levels, upto 50% above those of today on the Atherton Tableland (Kershaw & Nix1988), achieved between c. 5000 and 3500 b.p. On the Atherton Tablelandtemperatures also achieved high levels in this period; up to anestimated 3[degrees]C above those of today, they had risen from about1[degrees]C below present-day levels between 7500 and 6000 b.p. (Kershaw& Nix 1988). Despite highest temperatures and rainfall between 5000and 3500 b.p., there is evidence of increasing climatic variabilitybeginning around 5000 b.p., a time that corresponds with human presencewithin, and impact on, complex rainforest vegetation (McGlone et al.1992). The Holocene expansion of rainforest would have led to some greatersimilarities in habitat between New Guinea and northeastern Australiabut major floristic differences between the rainforest patches withinthis region (Barlow & Hyland 1988) suggest that it is unlikely thata continuous rainforest environment was ever created. The major extentof rainforest probably also occurred after the land connection betweenthe two islands had been severed c. 8000 b.p. (Torgersen et al. 1988). In central Australia Central Australia:see Northern Territory, Australia. higher levels of effective precipitation and amore complete vegetation cover are suggested from a cessation of sanddune sand duneHill, mound, or ridge of windblown sand or other loose material such as clay particles. Dunes are commonly associated with desert regions and seacoasts, and there are large areas of dunes in nonglacial parts of Antarctica. activity, generally between 8000 and 4000 b.p. (Ross et al. 1992),and by a greater abundance of tree pollen in the Lake Frome record,particularly between 6000 and 4500 b.p. (Singh & Luly 1991). Malleevegetation continues to replace chenopod shrubland in the NullarborPlain Nullarbor PlainVast limestone plateau, southern Australia. It lies along the south coast of western South Australia and eastern Western Australia, extending north from the Great Australian Bight to the Great Victoria Desert. through the Holocene until there is some reversal within the last5000 years (Martin 1973). At Lake Tyrrell Lake Tyrrell is a shallow, salt-crusted depression located in the Mallee district of north-west Victoria. It is approximately 70 square miles (180 square kilometers) in size and is located 195 miles (314 kilometers) northwest of Melbourne. Much of the time, Lake Tyrrell is dry. , mallee eucalypts andCallitris woodlands replaced Casuarina woodland between an estimated6600 and 2200 b.p. under inferred higher effective rainfall (Luly 1993).A summary of lake-levels for the interior of southeastern Australiaindicates low lake-levels until c. 7000 with maximum wetness around 4000b.p. before a gradual drying to present (Harrison & Dodson 1993). In southeastern mainland Australia, high moisture levels, centredon 6000 b.p., are indicated by maximum values for most woody taxa, andparticularly the rainforest taxon Nothofagus and the wet sclerophyllforest indicator, Pomadertis (Figures 5 & 6). Despite partialreplacement by Eucalyptus in some sites within the western part of theregion, Casuarinaceae values have increased, thanks largely to anincrease in sites from coastal environments, formed by the stabilizationof sea-levels at the end of the marine transgression. Despite theimportance of Casuarinaceae in western and coastal areas, there islittle response by the taxon to climatic changes in the southeasternhighlands at any time within the last 18,000 years. Its distributionthere must either be relict RELICT. A widow; as A B, relict of C D. , or else the taxon responds to climatesrepresented in other parts of the glacial cycle. Pomaderris shows highervalues in a range of sites than in any site today despite the fairlywide distribution of wet sclerophyll forest in the present landscape.Its altitudinal as well as spatial spread appears to indicate bothwarmer and wetter conditions than today, an observation made also fromits distribution at this time in Tasmania (MacPhail 1983); its limitedoccurrence in apparently suitable areas today suggests that some other,perhaps seasonal, aspect of the present-day climate, or anotherecological factor, is restricting its distribution. The past greater representation and broader distribution ofNothofagus forest has, like Pomaderris, generally been assumed toindicate maximum climatic amelioration, that included temperature aswell as rainfall. Based largely on such data, MacPhail (1979) consideredthat maximum effective precipitation occurred in Tasmania between 8600and 7000 b.p., consistent with lake-level highs for Tasmania at 7000b.p. (Harrison & Dodson 1993). Summer temperatures, although high atthis time, peaked about 1[degrees]C higher than today 6000 years ago,when the climate became slightly drier. Dodson et al. (1986) inferredmaximum rainfall and temperatures between 6000 and 3500 b.p. from thegreatest expansion of Nothofagus and wet sclerophyll forests on theBarrington Tops. However, from a predictive model of the present-dayclimate of Nothofagus (Busby 1986), Markgraf et al. (1986) calculatedthat temperature levels in Tasmania between 8000 and 6000 b.p., theirinferred rainfall peak, were somewhat lower than today, while McKenzieand Busby (1992) considered that the expansion of Nothofagus inVictoria, between 7000 and 4000 b.p., indicated only marginally higherprecipitation but substantially lower (2[degrees]C) summer temperatures.Winter temperatures may have been slightly higher, indicating lessseasonal variation than today. Markgraf et al. (1986) proposed an earlyHolocene temperature peak for Tasmania; this is supported by abioclimatic analysis of the aquatic taxon Brasenia which was growing inMorwell Bog within southern Victoria, well south of its presentAustralian range, c. 9000 b.p. (Lloyd 1991). Its presence suggests thatsummer temperatures were then at least 1.8[degrees]C higher than today. In lowland and coastal areas of southeastern Australia, most pollenand lake-level data indicate that maximum precipitation levels wereachieved between 7,000 and 5000-4500 b.p. Both older and youngerboundaries are marked by the initiation of peat growth as well as othersediment changes in the peatlands of the region (Figure 6). The olderlevel can be easily explained by increased precipitation and, in coastalareas, by a rise in the watertable as sea-level reached close to itspresent position. In many sites the younger level appears to be relatedto a reduction in stream flow which previously inhibited organicsediment accumulation and to a fall in lake-levels that speededsuccession from open water to swamp. The first records in southern Australia to indicate a mid-Holoceneoptimum were from southwestern Western Australia where an expansion ofEucalyptus diversicolor Karri (Eucalyptus diversicolor) is a eucalypt which is native to the wetter regions of south west of Western Australia. DescriptionThe tree grows to 90 metres, making it one of the tallest species in the world. (Karri karriNounpl -ris1. an Australian eucalypt2. its wood, used for building ) between 6000 and 4500 b.p. suggestedeffective precipitation higher than that of today (Churchill 1968).Surprisingly, re-examination of the main site, Boggy Lake, failed tosupport this reconstruction (Newsome & Pickett 1993). As in southeastern Australia, the latter stages of the marinetransgression resulted in the development of a complex of coastallandscapes including depositional environments conducive to theinvestigation of environmental histories around the coasts of otherparts of the continent. These histories have demonstrated rapidlychanging coast-line morphologies with the formation of extensive dunesystems and in-filling of estuaries. Perhaps the most dramatic andwell-studied changes have been in northern Australia. Estuaries withinthis region were marked by the development of extensive mangrove mangrove,large tropical evergreen tree, genus Rhizophora, that grows on muddy tidal flats and along protected ocean shorelines. Mangroves are most abundant in tropical Asia, Africa, and the islands of the SW Pacific. swampsbetween c.6800 and 5300 b.p. which subsequently gave way to a variety offreshwater swamp, woodland and forest communities (Woodroffe et al.1985; Tacon & Brockwell, this volume). Within areas of siliceous siliceousrelating to or made of silica or a silicate. sands, dune activity was marked until between 8500 and 7500 b.p. whendunes were stabilized, presumably by an increase in precipitation (Leeset al. 1990). The mid-to-late Holocene This review does not cover the Late Holocene, While most featuresof the present-day landscape had been established by c. 6000 b.p.,important changes have occurred since then. Reductions in vegetationcanopy cover, lower lake-levels and river flow velocities can beattributed to some decrease in effective precipitation. Others - morefrequent or intense burning, increases in sclerophyll, heath andpeatlands, and significant re-activation of desert dunes - suggestincreases in disturbance; they are frequently attributed to intensifiedhuman impact (e.g. Lourandos 1983; Head 1989). By an alternativesuggestion, there has been an increase in climatic variabilitythroughout the region, possibly beginning c. 5000 b.p. and becoming moreevident in the last 3000-4000 years (e.g. McGlone et al. 1992;Shulmeister & Lees in press; MacPhail A Hope 1985). General discussionData limitations The establishment of clear regional patterns ofenvironmental change is limited, primarily, by the distribution of theevidence. Most records are restricted to the more topographically andclimatically diverse eastern coastal and subcoastal areas with onlysparse and generalized information for the extensive inland plains. TheMurray Basin is a partial exception, but its moisture regime may relatemore to periodic conditions within the eastern highlands than to theclimates of the plains themselves. With a few possible exceptions inPapua New Guinea, no sites within the region have clearly provided acontinuous record through the whole period - the largest usual gap beingpart or all of the dry late glacial period. A number of sites containidentifiable unconformities; many others, particularly within organicsequences; may well contain undetected missing phases due to pastperiods of non-accumulation or peat wastage wastagea loss of product or productivity; in terms of animal production includes losses due to deaths of animals, lowered production from survivors, including reproduction, and lost opportunity income.wastageFetal wastage, see there through burning (Thomas& Hope 1994). Such gaps have a major influence on the establishmentof timescales, interpolated generally from a very limited number ofradiocarbon dates, and can easily explain many differences in timing ofclimate changes within and perhaps between regions. Periods ofnon-deposition and erosion also facilitate movement of carbon throughsediments and increase the chances of erroneous dates. The concentration of sites in areas of environmental heterogeneityhas a major influence on climatic inferences from pollen data. The mostsuccessful regional environmental reconstructions have been from pollendata in eastern North America and western Europe where, after themelting of ice caps, vegetation migrating great distances has producedsimilar signals despite locally variable environmental conditions. InAustralia, the lack of influence of extensive glaciation has produced,or allowed the survival of, a greater range of floristic elements, whoseresponses to climate change have differed. In the terms of Grichuk(1984), devised for the Russian flora, the basic types of flora inAustralia can be regarded as relict - characterized by an abundance ofold, relatively unchanging elements - and orthoselected - they have beenchanging in the same direction for a long time (primarily in thedirection of increased aridity or continentality, and in the Australiansituation, presumably due to fire). Migration floras, those which moveinto an area after elimination of the pre-existing flora due to glacialor periglacial conditions, are likely to be very limited in Australia. However, the well-documented nature of North American North Americannamed after North America.North American blastomycosissee North American blastomycosis.North American cattle ticksee boophilusannulatus. and Europeanvegetation has probably influenced the perception of how Australianvegetation responds to climate change. A number of authors (e.g. Nix& Kalma 1972; Horton 1982) show climatically zonal vegetation beltsmigrating thousands of kilometres towards and away from the arid centreduring glacial and interglacial in��ter��gla��cial?adj.Occurring between glacial epochs.n.A comparatively short period of warmth during an overall period of glaciation. periods respectively. The evidence, fromsoutheastern Australia at least, suggests more limited expansion andcontraction of elements that have survived in the region (see Figure 6).Nothofagus is a classic relict taxon, a survivor of the extensiverainforests of the Tertiary period. Its expansion during the Holocene'optimum' was probably limited by its poor migrational abilityand by fire, consequently the climatic signal from its distribution islikely to be subdued, areally limited and biased. The pattern ofdistribution of Eucalyptus and Casuarinaceae pollen during the height ofthe glacial period clearly indicates survival over much of the area,presumably in localized favourable patches. Subsequent increase has beenlargely by expansion from these retreats, rather than from migrationinto the area. The fact that Eucalyptus is still expanding, despite someclimatic deterioration in the last few millennia, suggests that it isadvantaged by the increasing levels of disturbance and/or climaticvariability, a typical response of an orthoselected taxon. Perhaps the taxa most likely to provide the most accuratepalaeoclimatic estimates are identifiable herbs and small shrubs thathave the ability to migrate large distances. The alpine and sub-alpinespecies from Spring Creek macrofossils and pollen of the themonospecific monospecific/mono��spe��cif��ic/ (mon?o-spe-sif��ik) having an effect only on a particular kind of cell or tissue or reacting with a single antigen, as a monospecific antiserum. genus Brasenia from Morwell Bog, all taxa recorded outsidetheir present-day ranges, would fall into this category. A major problem in estimating palaeoclimates from total pollenassemblages, which is related to different floral responses, is the lackof present-day analogues, at least for older time-periods. A comparisonof fossil pollen spectra covering the last 18,000 years from NorthwestCrater at Tower Hill in Victoria, with all recent pollen spectra fromthe southeast Australian data-base, revealed the existence of vegetationlacking modern analogues until c. 6000 b.p. (Kershaw & Bulman inpress). The mid-Holocene expansion of Pomaderris would also indicate alack of analogues for the eastern highland region for this time. It isdifficult to assess the degree to which no-analogue vegetation is theresult of the dynamics of the vegetation or the presence of climatesdifferent from those of today. As well as providing direct evidence of past climates and resourcesfor human habitation HABITATION, civil law. It was the right of a person to live in the house of another without prejudice to the property. 2. It differed from a usufruct in this, that the usufructuary might have applied the house to any purpose, as, a store or manufactory; whereas , vegetation makes an important contribution tolandscape stability and the hydrological hy��drol��o��gy?n.The scientific study of the properties, distribution, and effects of water on the earth's surface, in the soil and underlying rocks, and in the atmosphere. system. While there isfrequently no easy way of assessing the degree of vegetation cover frompollen data, it may be a key to reconciling the conflicting evidence foractive desert dunes and apparently high lake water levels during thelast glacial in some areas. At Boulder Swamp in East Gippsland, the lateglacial alluvial sediments suggest that this was the period of highestfluvial activity, while pollen data indicate the presence of a lesscomplex and more unstable vegetation cover than during the Holocene.This would have facilitated erosion and transport of a high and coarsesediment load (Kenyon 1989). Regional patterns and causal mechanisms Palaeoecological data are used to test the reliability of, and torefine, large-scale simulations of past environments, particularlyclimate. Conversely, where there is good correspondence between themodels and the data, the models can be used to predict conditions inareas that have poor paleoenvironmental coverage, and to provide causalmechanisms for all resultant patterns. The most recent and comprehensive simulation of Australianterrestrial climates is contained in the global model of COHMAP COHMAP Cooperative Holocene Mapping Project (1988;see also Wright et al. 1993) which has been compared with proxy datafrom the region (Harrison & Dodson 1993). Additional proxy data andmore generalized models available since this time allow some furtherassessment of the COHMAP simulations. During the height of the last glacial period temperatures wereprobably around 4 to at least 6 [degrees] C lower than today throughoutthe southern part of Australia, and of a similar order in the Highlandsof New Guinea, both lower than the COHMAP predictions.(2) The COHMAP model indicates little variation in precipitationthrough the period of interest. In southern Australia it is possiblethat, from proxy data, there has been some over-estimation of the degreeof aridity during the height of the last glacial period. Part of theassumption of glacial aridity, in southeastern Australia at least, isthat sedimentary and pollen records often terminate at the base of theHolocene. This is perhaps more a reflection of late glacial aridity thandry conditions during the glacial proper. Water was certainly present ina number of southeast Australian lakes during the glacial. Lakes in thesoutheastern interior were high, at least for part of the period, butthis could have been as much due to higher water-tables or directrun-off from melting snow in the highlands as to direct precipitation.There is little doubt that, in the tropical lowlands, the glacial periodwas dry. Here evaporation rates are likely to have been much higher, dueto a lesser reduction in temperature, than in the south. The COHMAP model, in common with previous reconstructions (e.g.Rognon & Williams 1977; Markgraf et al. 1992), shows an expandedsubtropical sub��trop��i��cal?adj.Of, relating to, or being the geographic areas adjacent to the Tropics.subtropicalAdjectiveof the region lying between the tropics and temperate lands high-pressure belt over Australia with a poleward shift ofthe westerlies, by up to 8 [degrees], in winter, considered consistentwith the orientation of glacial desert dunes and drier conditions overmuch of the southern part of the continent including Tasmania (HarrisonA Dodson (1993). However, the proposal here - that conditions may nothave been as arid as previously thought (substantially drier conditionsfor Tasmania are based on very thin data) and that winters are likely tohave been wet - would tend to support other proposals (e.g. Bowler 1975;Harrison et al. 1984) that the westerlies were situated closer to theequator. Perhaps there is little reason to postulate postulate:see axiom. , from Australiandata at least, any significant change in the mean position of thepressure belts; there may have been greater seasonal movement with thewesterlies extending further north than today during the winter. Any netdecrease in effective precipitation may be accounted for by cooleroceans and a higher degree of continentality. In the north of thecontinent, increased aridity would result from the extensive drycontinental shelf areas and some reduction in sea-surface temperatures. The data indicate that effective precipitation was lowest for thewhole period during all or part of the late glacial throughout theregion. The lack of evidence for peat formation anywhere, except perhapsin perhumid parts of New Guinea, indicates a lack of permanentwater-bodies over most of the present extent of the continent. Woodlandor forest development in the higher parts of southeastern Australia fromc. 13,000 b.p. together with some evidence for periodic high fluvialactivity suggests, however, that there may have been significantseasonal water in these areas. Drier conditions in the south areconsistent with the COHMAP simulation for a further pole-ward expansionof the sub-tropical high-pressure belt c. 12,000 b.p. and may suggestalso an equator-ward expansion. The effect of rising sea-levels andsea-surface temperatures would have been nullified nul��li��fy?tr.v. nul��li��fied, nul��li��fy��ing, nul��li��fies1. To make null; invalidate.2. To counteract the force or effectiveness of. by increasedevaporation as a result of increasing land temperatures. There are indications of most rapid climate change around thePleistocene-Holocene transition with marked altitudinal rises in thevegetation belts of New Guinea and the southeastern highlands ofAustralia reflecting a rise in temperature to levels at or above thoseof today in many areas shortly after 10,000 b.p. This pattern oftemperature change is very similar to that in other regions includingNorth America and Europe (Webb et al. 1993). The simulated seasonaltemperatures of COHMAP for 9000 b.p. are at variance with the availableevidence. These simulations emphasize the importance oforbitally-related solar input which suggests little seasonality, withsummer temperatures lower than those of today. Yet the evidence fromMorwell Bog in the Latrobe Valley indicates high summer temperaturessimilar to those predicted for the Northern Hemisphere. Higher, ratherthan lower seasonality is also inferred from closest modern`analogues' to Tower Hill. These `analogues' suggest a moremediterranean-type climate at this time. Clearly there is a need for agreat deal more data and analysis to resolve such discrepancies. More data are also required to further test the proposition thatthere was a switch from winter to summer rainfall across the centrallatitudes of Australia in the late Pleistocene or early Holocene assuggested from the Lake Frome data (Singh 1981; Singh & Luly 1991).On the assumption that tropical taxa are going to become increasinglyimportant as temperatures rise through this period, regardless of theseasonal distribution of rainfall, the argument essentially rests on anincreasing proportion of grasses to chenopods in the understorey.However, a similar change in the proportions of these taxa is recordedbetween 12,000 and 9000 b.p. in the southeastern Australian database(see Figure 5), an area that is unlikely to relate to the seasonalrainfall boundary. This change is interpreted as a regional increase inrainfall. The reason for a shift in the rainfall boundary would be theinitiation or intensification of the monsoon system., such acirculation, well marked in the northern African region from c. 12,000b.p. (Kutzbach & Street-Perrott 1985), there can be explained bystrong land/sea temperature contrast and a source of moisture. InAustralia the still exposed continental shelves in the northern sourcearea are unlikely to have allowed an intense monsoon system; relativelydry conditions are maintained in northern Australia until c. 8000-7000b.p. A reversal of the grass/chenopod ratio in the late Pleistocenearound Lake Frome is also registered in southeastern Australia where themost economical interpretation is simply a reduction in moisture levelsor greater climatic variability, rather than any substantial shift inseasonal rainfall patterns. Little can be inferred about the existence of a Younger Dryas eventin the region. There is some recent supporting evidence for it in thenorthern part of the region but the absence or condensed nature ofsediments in most sites at the very end of the Pleistocene period makeits investigation extremely difficult. Available quantitative estimates of temperature are in agreementwith COHMAP predictions for the period centred on 6000 b.p., despite thevariance of the estimates for 9000 b.p. Both on the Atherton Tablelandand in the eastern Highlands of Victoria, BIOCLIM estimates indicatetemperatures lower than today with less seasonal variation (Busby 1991).These estimates are in direct conflict with the general belief thattemperatures peaked with effective precipitation between c. (8000-7000and 5000 b.p., a belief reiterated by Harrison & Dodson (1993).There is no obvious explanation, from a consideration of the globalpattern of solar insolation, of a marked decline in temperature between9000 and 6000 b.p. in the Southern Hemishere. This led Kershaw (1993) toconsider that the apparent reduction in temperature, within the highrainfall Atherton and Central Highlands region, was a localized resultof the moderating effect of increased cloud cover, a parameter notincluded in the BIOCLIM model. The high correspondence between theseBIOCLIM temperature estimates and the COHMAP model may be fortuitous. The increase in precipitation to the mid-Holocene peak is explainedfor southern Australia by a gradual equatorial shift in the southernmargin of the subtropical high-pressure belt to north of its presentposition, increasing the influence of westerlies throughout the year(Harrison & Dodson 1993). The pattern would no doubt be augmented bydecreased seasonality with sea-level rise and warming ocean surfacewaters. In the northern part of the continent, wetter conditions wouldresult from the flooding of the extensive continental shelves, with thedevelopment of a monsoon system helping to transport the moistureinland. Conclusions At a very general level, the whole of Greater Australia may haveexperienced similar climatic trends in environmental change through thelast 18,000 years. The cold last glacial period experienced lowerrainfall than today but its effectiveness, particularly at higherlatitudes, was still significant. High seasonality during this periodappears to have excluded extensive tree survival over much of southernAustralia. These two factors may have combined to produce a veryunstable landscape. Temperature rise preceded a rise in precipitationduring the `late glacial', resulting in widespread arid conditionscentred on 12,000 b.p. The most rapid changes occurred between 12,000and 9000 b.p., although there is little evidence for a Younger Dryasreversal in climatic amelioration. During this time forest andparticularly woodland expanded in southern Australia. Highesttemperatures may have been achieved in the very early Holocene before apeak in effective precipitation in all areas at some time between about8000 and 4000 b.p. This peak was accompanied by major expansions ofrainforest and wet sclerophyll forests in wetter areas and a furtherspatial expansion of open forest. Both precipitation and temperaturedeclined after this time with some subsequent minor fluctuations, but amajor feature of the late Holocene has been the development of climaticvariability. General directions, if not the magnitude, of change are largelypredictable from a consideration of the direct effects of ice-capmelting and associated sea-level rise and orbital changes in solarradiation as well as atmospheric circulation changes resulting fromthese changes in sea-level and temperature. However, data limitationsrelated to a sparse and geographically biased distribution of sites,generally coarse temporal resolution of records and lack of recordquantification in vegetation and climatic terms prohibit properinvestigation of some potentially interesting local and regionalvariation.Acknowledgements. I thank Dave Bulman for undertaking much of theanalysis of the southeastern Australian pollen data, Jim Allen, GeoffHope and run O'Connell for valuable comments on a draft of themanuscript, and Gary Swinton and Phil Scamp (Special Computer APL Machine Portable) IBM's first single-user computer. Built within a six-month period and introduced in 1973, SCAMP was the prototype of the 5100 series that was launched two years later. See 5100. for production of the textfigures.(2) The COHMAP model used the CLIMAP sea-surface temperature estimates;as previously mentioned, the difference between mountain and sea-surfaceestimates from the tropics has not been explained satisfactorily. 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